In order to more rapidly heat the catalyst in the exhaust system of an internal combustion engine during cold start conditions, the ignition timing may be significantly retarded to provide increased heat flow to the exhaust system. The increased heat flow to the catalyst allows it to function sooner to decrease undesirable emissions. Moreover, by retarding the spark timing during extended idling periods, the consequent sustained reduction in heat flow to the exhaust system is avoided, preventing the catalyst from cooling and becoming less efficient.
Conventional closed loop fuel control systems are responsive to the sensed level of oxygen in the combustion gases produced by the engine as measured by an exhaust gas oxygen level sensor. The controller responds to a lean condition by progressively increasing the fuel delivery rate until a rich condition is detected, then decreases the fuel delivery rate until a lean indication appears, and so on. In this way, the closed loop controller cart maintain the air/fuel mixture at or near stoichiometry to minimize undesirable combustion products.
The fuel control system achieves the desired air/fuel ratio more rapidly when the open-loop portion of the system is able to accurately predict the needed air/fuel ratio based on sensed engine operating conditions (engine speed, load) etc. Adaptive control systems better achieve this accuracy while accommodating production variations in airflow measuring and fuel metering devices used in different engines, by storing parameters developed by the closed loop controller for future use. During subsequent engine operations, the previously generated and stored parameters are retrieved to enable the closed loop controller to more rapidly and more accurately achieve desired air/fuel ratios.
After successful adaptation by the fuel control system, the engines ability to operate at optimal, leaner air/fuel ratios is significantly improved. However, until such adaptation is achieved, the ability of a given engine to provide good driveablility with significantly retarded spark timing is problematic.